New Experimental 23Na(α, p)26Mg Reaction Rate for Massive Star and Type Ia Supernova Models

N J Hubbard,O S Kirsebom,S P Fox,M Munch,H O U Fynbo,A M Laird,M Pignatari,C Aa Diget,J R Tomlinson,A M Howard,A Parikh

doi:10.3847/1538-4357/abee91

Abstract

Abstract The 23Na(α, p)26Mg reaction has been identified as having a significant impact on the nucleosynthesis of several nuclei between Ne and Ti in Type Ia supernovae, and of 23Na and 26Al in massive stars. The reaction has been subjected to renewed experimental interest recently, motivated by high uncertainties in early experimental data and in the statistical Hauser-Feshbach models used in reaction rate compilations. Early experiments were affected by target deterioration issues and unquantifiable uncertainties. Three new independent measurements instead are utilizing inverse kinematics and Rutherford scattering monitoring to resolve this. In this work we present directly measured angular distributions of the emitted protons to eliminate a discrepancy in the assumptions made in the recent reaction rate measurements, which results in cross sections differing by a factor of 3. We derive a new combined experimental reaction rate for the 23Na(α, p)26Mg reaction with a total uncertainty of 30% at relevant temperatures. Using our new 23Na(α, p)26Mg rate, the 26Al and 23Na production uncertainty is reduced to within 8%. In comparison, using the factor of 10 uncertainty previously recommended by the rate compilation STARLIB, 26Al and 23Na production was changing by more than a factor of 2. In Type Ia supernova conditions, the impact on production of 23Na is constrained to within 15%.

Highlights

The 23Na(a, p)26Mg reaction rate has been the subject of a number of nuclear astrophysics studies in the last decade
In the present paper we show that when corrected for the angular distributions presented, these measurements are all consistent to within 30% with one another in the energy range Ecm = 1.7–3.0 MeV
The angular distributions of the emitted protons produced by the 23Na(a, p)26Mg reaction were measured at Aarhus University, Denmark as part of the direct measurement of the cross sections, and the experimental setup is described in detail by Howard et al (2015)

Summary

Introduction

The 23Na(a, p)26Mg reaction rate has been the subject of a number of nuclear astrophysics studies in the last decade. The angular distributions have been obtained from the data taken at Aarhus University (Howard et al 2015), which can be applied to the other data sets to eliminate angular distribution assumptions, reducing systematic uncertainties on their crosssection measurement, and ensuring consistency across the three measurements These new angular-distribution-corrected measurements have been combined to obtain a new recommended experimental astrophysical reaction rate, with a significantly reduced uncertainty. The impact of this rate has been modeled in massive stars and Type Ia supernova

Experimental History

Experimental Angular Distributions

Experimental Reaction Rate

Findings

Summary